Memory chips, fingerprints, iris scans ... but will it work?

The results of initial trials of biometric technology - the electronic facial images, fingerprint and iris scans that underpin the identity card scheme - leave question marks over its effectiveness.

While the enrolment trial involving 10,000 volunteers showed that the iris scans were successful in 96% of cases, facial images and electronic fingerprints were far less effective. The tests also showed that black people and those over the age of 59 had lower success rates when they were enrolled in the scheme using scans of their eyes.

Ministers insisted that the trial was not a test of the technology but was about studying people's experiences and attitudes towards the scheme.

The main findings of the trial show that most of the people were comfortable with the new process, and felt that the booths provided were sufficiently private and that it was quite quick, with an average time of about eight minutes for all three biometrics.

But the scale of the national identity card scheme, which will see 44 million people over the age of 16 enrolled, means there will be questions concerning the effectiveness of the new technology.

Ministers said yesterday that the biometric technology was already being used in the Gulf states - but Britain's ID card scheme, with an overall cost passing the £5.8bn mark, meant that it would be the largest public sector IT project in Europe.

Although the trial was not a test of the technology it showed that there were still problems with individual types of biometrics.

For the test, each volunteer sat down on a chair in a booth. There was a camera mounted on the wall, and an electronic signature pad and fingerprint device on the desktop. The test covered both initial enrolment and verification for each biometric.

While there were high rates of success, of 90% or more for enrolment on all three types of biometric, the results for the verification varied. For the facial biometric - which measures the distance between various points on the face - the success rate was 69% overall and only 48% for disabled people who took part. Iris verification was better, with a 96% success rate. But fingerprint verification fell to 81%, with problems occurring with the machine recording enough detail from the fingers.

The Home Office minister Tony McNulty, said the failure rates were partly the reason the decision had been taken to incorporate all three forms of biometric on the identity card/passport.

"Those who know far better than I say things are going in the right direction," he said. "The combination of the three biometrics add to the integrity of the process. Some say that goes too far."

The number of biometric identifiers included on the identity card depends on memory space on its computer chip and so is a question of cost. The European Commission has said that, ideally, all 10 digits on both hands should be included to reduce the number of "false positive" identifications and other errors. But that is regarded as the "Rolls-Royce" solution and it is more likely that the cheaper option of two digits will be used.

The scale of the ID card project in Britain is daunting in terms of the history of Whitehall computer projects.

The success of the recent Airwave police radio computer project has been outweighed by big problems experienced at the Criminal Records Bureau with inputting data.

The UK Passport Service, which is to lead on the ID card project, has had own computer problems in the 1990s.